The fossil record from the Ediacaran Period is sparse, as more easily fossilized hard-shelled animals had yet to evolve. The Ediacaran biota include the oldest definite multicellular organisms (with specialized tissues), the most common types of which resemble segmented worms, fronds, disks, or immobile bags. Auroralumina was a cnidarian.[31][32] Most members of the Ediacaran biota bear little resemblance to modern lifeforms, and their relationship even with the immediately following lifeforms.